A study on natural clinoptilolite for CO2/N2 gas separation

Based on its low cost and low water adsorption capacity, compared to synthetic zeolites (A-type, X-type and Y-type), natural, untreated clinoptilolite was examined as a potential adsorbent for a separation process targeting on removal of CO₂ from flue gas. Taking into consideration typical flue gas composition and temperature, adsorptive properties of binary CO₂/N₂ mixtures were tested in the temperature range of 268 to 403 K and compared with literature data. The results showed that CO₂ concentration, total pressure, and temperature strongly affect selectivity and working capacity, restricting the conditions under which the material could be used as an efficient adsorbent.     

Economic ordering policy for an item with imperfect quality subject to the in-house inspection

This article considers a production/inventory system where each lot of items received or produced contains a random proportion of defective units, items of imperfect quality. The purchaser contacts a 100% inspection in order to identify the perfect (acceptable) quality items. The model examines the following two options for the imperfect quality items: sell them to a secondary market, as a single batch and at a price lower to that of new ones, or rework them at some cost and then use them as new ones to satisfy demand. After inspection, the good quality items are sent to the working inventory warehouse in batches of equal size. For both of these cases, the optimal ordering lot size and the optimal number of batches are obtained. A numerical example illustrates the solution procedure and sensitivity analysis results are reported.     

Tensile behaviour of as deposited and heat-treated electroless Ni-P deposits

Electroless Ni-P coatings were deposited on mild steel substrates and the effect of heat-treatment on their structure and tensile behaviour was studied, with the following conclusions. The as-deposited electroless Ni-P coating is amorphous and it remains amorphous up to 300 °C. At 400 °C the coating becomes crystalline and consists of a Ni₃P matrix containing areas of metallic nickel. For the selected coating/substrate thickness ratio, the contribution of the coating in the tensile properties of the coating-substrate system is negligible as expressed by the values of yield strength, ultimate tensile strength and fracture strain in mild steel substrates and coated as-deposited and heat-treated specimens. Extensive cracking of the coating accompanied by spalling was occurred during the tensile tests. The density of cracks was found to increase close to the fracture surface of the tensile specimen and with increasing heat-treatment temperature. The cracks observed on the surface of the coatings are believed to form due to the inability of the brittle coating to accommodate the strain generated in the ductile substrate. Their orientation to the tensile axis is in close relation to the structure of the coating and the failure mechanism that is dictated by this structure. The first cracks on the surface of the coatings were found to form after the yield strength of the tensile specimen has been reached and plastic deformation of the substrate takes place. Their density increases with the accumulation of strain up to fracture.     

Fumigant toxicity of three essential oils on the eggs of Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae)

Fumigant toxicity of the essential oils from Lavandula hybrida, Rosmarinus officinalis and Eucalyptus globulus against the eggs of Acanthoscelides obtectus was assessed. The essential oil vapours were toxic to eggs with LC₅₀ values ranging between 1.3 and 35.1 μl/l air, depending on egg age and the essential oil. In all cases, the young eggs (3-day old) were more tolerant to essential oil vapours than the older ones (4-day old). Apart from the inhibition of hatching, the exposure of eggs to essential oil vapours increased the subsequent mortality of hatched larvae. The influence of length of exposure to essential oil vapours on egg hatchability was also significant.     

Supply chain models for deteriorating products with ramp type demand rate under permissible delay in payments

In this paper an order level inventory model for deteriorating items with general ramp type demand rate under conditions of permissible delay in payments is proposed. In this model shortages are allowed and partially backlogged. The backlogging rate is variable and dependent on the waiting time for the next replenishment. Its study requires exploring the feasible ordering relations between the time parameters appeared, which leads to three models. For each model the optimal replenishment policy is determined. The sufficient conditions of the existence and uniqueness of the optimal solutions are also provided. Suitably selected numerical examples highlight the obtained results. Sensitivity analysis of the optimal solution with respect to major parameters of the system has been carried out and the implications are discussed.     

Assessing the performance of short multi-item questionnaires in aesthetic evaluation of websites

In recent years, website aesthetics has received a fair amount of attention from the HCI community. This has led to the creation of a variety of multi-item questionnaires aimed at capturing users’ aesthetic judgments. Researchers have used these questionnaires in several HCI studies to investigate the relationship between aesthetics and other evaluative constructs such as usability. However, their usefulness as evaluation tools in visual design practice remains underexplored. Lengthy multi-item questionnaires can be particularly problematic especially in studies where participants must evaluate multiple designs or when they are required to give responses repeatedly in predefined time intervals. Despite the criticism, single-item scales have been used in many past studies in which questionnaire length could be problematic. Another alternative available to practitioners/researchers are short versions of standardised multi-item questionnaires that have been created for the aesthetic evaluations of websites. In this paper, we present a study in which we compare the performance of three such condensed aesthetic questionnaires (i.e. aesthetics scale, AttrakDiff, VisAWI) during a website redesign project. The short versions of those questionnaires were used by 187 users during an evaluation of 7 alternative website designs. The questionnaires were compared on performance criteria such as reliability, validity, and predictive ability. Data analysis showed that although AttrakDiff’s overall performance was better, a considerable amount of variance in aesthetic judgment could not be accounted for by any of the questionnaires.     

Measuring regional economic efficiency: the case of Greek prefectures

This paper, using Data Envelopment Analysis (DEA), measures for the first time the economic growth policies of the Greek prefectures. Based on the neoclassical model of growth it uses private and public investments and labour force as inputs and GDP per capita as output for the time period of 2003–2006. The results indicate that there are significant regional policies inefficiencies among the Greek prefectures. Additionally, growth inefficiencies within the 13 administrative regions are reported. Finally, the analysis provides benchmarks for policy evaluation and suggestions for region-based approaches to growth problems.     

A periodic-review inventory model in a fluctuating environment

We study a single-item periodic-review inventory model in a fluctuating environment with a fixed lead time of λ periods. The state of the environment at the beginning of each period is described by a homogeneous Markov chain. Ordering, holding, penalty costs and the distributions of random variables representing the customer's demand and the supplier's capacity level are state environment dependent. By using dynamic programming it is proved in the finite-horizon case that the optimal policy is of a base stock type. Its parameters are monotonic in the number of the periods making up the horizon and also in stochastically ordered random variables representing different supplier capacities. Similar results are proved for the infinite-horizon problem.     

Design of corrugated optical waveguide filters through a direct numerical solution of the coupled Gel'fand-Levitan-Marchenko integral equations

Regarding the design problem of corrugated planar optical waveguide filters, a new numerical method is presented consisting of a direct numerical solution of the coupled Gel'fand-Levitan-Marchenko integral equations. This method, which uses leapfrogging in space and time, is exact in principle and avoids some difficulties encountered in previously derived analytical methods of solution. Straightforward numerical calculations permit the design of several classes of filters such as Butterworth, Chebyshev, Cauer (elliptic) and others, as presented in the paper. The accuracy of our proposed method of design is checked in several ways, mainly through the numerical solution of the corresponding direct-scattering problem (Riccati differential equation).     

The corrosive wear of nickel coating on mild steel

The abrasive wear of nickel coatings on steel substrates, under corrosive conditions was studied. For specimens with and without heat treatment, the wear rate was observed to depend upon the nature of the corrosive solution. The composition of the wear debris was noted to be a function of the corrosive wear conditions. The wear rate of the heat treated specimens was observed to be lower than that of the non-heat treated nickel-coated steel specimens.